The objective of the project is a quantitative evaluation of tumorigenesis of polycyclic aromatic hydrocarbons in relation to the extent of binding of these compounds to DNA. The biological systems elected for this study are the newly investigated rat-liver nuclei and the mouse skin. The enzymic capacity of purified rat-liver nuclei to bind carcinogens to nuclear DNA will be pursued. In addition to the accomplished experiments with hydrocarbons, binding of other classes of carcinogens to nuclear DNA will be studied. The nature of the enzymes invlved in carcinogen activation will be investigated by correlation of binding with aryl hydroxylase(AHH) activity in the nucleus. The extent of DNA,RNA, and protein in mouse skin in function of AHH inducers and inhibitors will be determined by means of an improved assay method for the AHH activity. Besides, the skin and the purified liver nuclei will be used for elucidation of the chemical nature of the DNA-hydrocarbon bond. The results should provide evidence of the mechanism of binding and define the significance of the interaction between hydrocarbon and DNA in the process of tumor initiation.